Ink jet printing processes generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet printing systems, ink is emitted in a continuous stream under pressure through an orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the nozzle. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a specific location on a recording medium or to a waste ink collecting recipient. In the non-continuous process, or the so called "drop-on-demand" systems, a droplet is expelled from a nozzle to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
The most important part of an ink used in ink jet printing are the dyes. Although a number of dyes have been proposed none has been produced which meets all the requirements of a modern printing process.
C.I. "Food Black 2" (formula I) and dyes having similar structures have been mentioned as black dyes for ink jet printing inks in JP Patent Application 59-093'766. These dyes, however have a somewhat bluish hue and give images with poor light fastness. ##STR3##
Reactive black dyes have also been proposed for ink jet printing for example in the Patent Application EP 0,693,537. However, inks containing dyes with incorporated reactive groups deteriorate the storage stability of the inks and due to their potential health risk they are not particularly suitable for handling in a non chemical environment.
Black type recording liquids using "Pacified Reactive Black Dyes" are described in U.S. Pat. No. 5,725,641. It relates to ink compositions comprising the metallized azo dye "Reactive Black 31" in either or both of its hydrolysed forms according to general formula (II) ##STR4##
where X is CH.sub.2 CH.sub.2 OH and/or CH.dbd.CH.sub.2. PA1 wherein D is substituted phenyl or naphthyl; R.sub.1 is hydrogen, alkyl or alkoxy with 1 to 4 C atoms, NHCONH.sub.2 or NHCOR.sub.3 where R.sub.3 is alkyl with 1 to 4 C atoms; R.sub.2 is hydrogen or unsubstituted or substituted phenyl and Met is copper or nickel. PA1 wherein A represents phenyl or naphthyl having one or more sulpho groups; m is 0 or 1 with the proviso that m is 1 when n is 0 and m is 0 when n is 2. PA1 wherein Met is copper, nickel, zinc or iron; Q is a substituted or unsubstituted phenyl or naphthyl group and Z is hydrogen, lower alkyl, lower alkoxy, sulpho, and substituted or unsubstituted amino. The hue of all these metallized dyes is greenish blue to blue. PA1 wherein Met represents copper, nickel, zinc or iron. However, all of the disclosed compounds are giving red to blue hues and yellow, red, orange or other dyes need to be added to provide a black colour. PA1 A is unsubstituted or optionally substituted phenyl or unsubstituted or optionally substituted naphthyl; PA1 R.sub.1 is hydrogen, alkyl, optionally substituted alkyl, alkoxy, optionally substituted alkoxy, all with 1 to 18 C atoms, amino, optionally substituted amino, halo, trifluoromethyl, carboxy, sulpho, carbamido, alkylcarbonylamino, arylcarbonylamino; or forms together with R.sub.2 and the phenylene ring a 1,4-naphthylene moiety, which can be unsubstituted or substituted in position 6 or 7; PA1 R.sub.2 is hydrogen or forms together with R.sub.1 and the phenylene ring a 1,4-naphthylene moiety, which can be unsubstituted or substituted in position 6 or 7; PA1 R.sub.3 is hydrogen, alkyl, optionally substituted alkyl, all with 1 to 18 C atoms, cycloalkyl, unsubstituted or optionally substituted heterocyclic alkyl, unsubstituted or optionally substituted aryl, unsubstituted or optionally substituted aralkyl, saturated and unsaturated aza and/or oxa and/or thia heterocyclic radicals; PA1 M is hydrogen, a metal cation, preferentially an alkali metal cation, an ammonium cation or an ammonium cation substituted with alkyl, alkoxyalkyl or hydroxyalkyl radicals each having 1 to 12 C atoms; and PA1 Met is Cu, Ni, Zn or Fe with the proviso that Met is Cu, Ni or Zn if the metallized bisazo dye is of general formula (IX) and Met is Fe if the metallized bisazo dye is of general formula (X). PA1 wherein A, R.sub.1 and R.sub.2 are defined as above and R.sub.4 is hydrogen, halogen, hydroxy or alkoxy, is diazotized by ordinary methods well known in the art, PA1 wherein R.sub.3 is as defined above, and PA1 wherein A, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined above. PA1 A: A bisazo compound of general formula (XIII), wherein R.sub.4 is methoxy, when heated in the presence of cuprammonium sulphate and an alkanolamine undergoes a copper promoted dealkylation to give the corresponding Cu-metallized bisazo dye of general formula (IX). PA1 B: A bisazo compound of general formula (XIII), wherein R.sub.4 is halogen undergoes hydrolytic coppering to give the corresponding Cu-metallized bisazo dye of general formula (IX). PA1 C: A further used method, known as oxidative coppering and described for example in Angewandte Chemie 70, 232, 1958), Patents DE 900,600 and DE 1,006,098, requires as starting material a bisazo compound of general formula (XIII), wherein R.sub.4 is hydrogen. PA1 D: Fe-metallized bisazo dyes of general formula (X) for example can be prepared according to U.S. Pat. No. 5,376,151 by reacting two equivalents of a compound of formula (XIII), wherein R.sub.4 is hydroxy, with one equivalent of an Fe(II) or an Fe(III) salt at a slightly alkaline pH.
These inks are claimed to be lightfast and to possess reliable ink jet pen performance.
The pacification process is accomplished by making an aqueous solution of "Reactive Black 31". The aqueous solution is heated to 60.degree. C. and the dye is hydrolysed by addition of sodium hydroxide in amounts sufficient to bring the pH of the solution to a range of about 8 to about 12. After the completion of the hydrolysis the pH of the solution is lowered to about 7 with hydrochloric acid. The recording liquids in U.S. Pat. No. 5,725,641 are required to contain less than 1 wt % of sulphate ions, preferably less than about 1000 parts per million. Thus the sulphate ions generated during the hydrolysis reaction and the chloride and sodium ions added during the process have to be removed in an additional purification step. Further, to compensate the reduced water solubility of the dyes of general formula (II) compared to the initial "Reactive Black 31", 10 to about 40 wt %, preferably 20 to about 25 wt %, of at least one organic solvent are required to provide inks with the claimed performance. Furthermore, on exposure to light, images on a range of recording materials suffer from colour shifts when printed with ink jet inks containing "Reactive Black 31" or "Pacified Reactive Black 31".
In Patent Application EP 0,662,499 ink jet inks using either metallized or non-metallized azo dyes are disclosed. Dyes preferentially used for black recording liquids were "Acid Black 51" (Formula III) and/or "Reactive Black 1" (Formula IV). ##STR5##
However, both of these black metallized azo dyes are based on metal ions, such as chromium ions, which are presently regarded by the United States Regulatory Authorities as priority pollutants.
In Patent Application DE 3,236,238 1:1 metallized bisazo dyes of general formula (V) are claimed as being useful for dyeing and printing of cellulose containing materials in blue shades ##STR6##
In Patent Application EP 0,632,105 metallized bisazo dyes of general formula (VI) are claimed as blue dyes for dying paper making material and cellulose fibres ##STR7##
In Patent Application EP 0,593,324 metallized bisazo dyes of general structure (VII) are claimed and polarising films having said dyes incorporated therein are described ##STR8##
In U.S. Pat. No. 5,639,809 polarising films containing metallized bisazo and trisazo dyes of general formula (VIII) have been described, ##STR9##
Metallized azo dyes with structures mentioned above considered to be state of the art do not satisfy all the required demands when used in aqueous inks for ink jet printing.
Dyes used for such recording liquids have to be sufficiently soluble in water and typical ink liquids, should not show bronzing on recording materials (association of dye on the surface of the recording material), they have to be stable even when the recording liquid is stored for long periods of time, they need to provide printed images having high optical density, excellent water fastness and excellent light fastness. Various types of compositions have been proposed as inks for use in ink jet printing. Typical inks are composed of various types of dyes, water, organic solvents, cosolvents and other additives.
In particular the inks have to meet the following criteria:
(1) The ink gives high quality images on any type of recording medium. PA0 (2) The ink gives printed images exhibiting excellent water fastness. PA0 (3) The ink gives printed images exhibiting excellent light fastness. PA0 (4) The ink does not clog jetting nozzles even when these are kept uncapped while recording is suspended. PA0 (5) The ink is quickly fixed onto recording media without bronzing and can not therefore be scrubbed off. PA0 (6) The ink can be stored for a long period of time without deterioration in its performance. PA0 (7) Physical properties of the inks, such as viscosity, conductivity and surface tension, are each within a defined range. PA0 (8) The recording liquid has to be safe, non toxic and not flammable. PA0 (I) An amine of general formula (XI) ##STR12## PA0 (ii) coupled under alkaline conditions with a compound of general formula (XII) ##STR13## PA0 (iii) metallizing the resulting bisazo dye of general formula (XIII) ##STR14##